Recently, we reported the discovery of a new reaction in which a cyclic anhydride randomly inserts into carbon-oxygen bonds of a polyether to generate a polymeric composition having both ether and ester functionalities (see application Ser. No. 07/979,760, now U.S. Pat. No. 5,319,006). A Lewis acid such as zinc chloride or zinc bromide catalyzes the reaction.
When a polyether polyol reacts with a cyclic, saturated anhydride, for example, the product is a saturated polyetherester polyol useful for polyurethane applications. Cyclic, unsaturated anhydrides such as maleic anhydride can be used in the process to make unsaturated polyetherester resins. The unsaturated resins can be reacted with vinyl monomers to produce cured polyetherester products.
Compared with the synthesis of conventional unsaturated polyester resins, the process for making polyetheresters by anhydride insertion has great flexibility. The average polyether chain length between ester linkages and the crosslinkability of the polyetherester are controlled by simply adjusting the proportion of cyclic, unsaturated anhydride used. Products having a wide range of unsaturation levels are available from a single polyether polyol and a single cyclic, unsaturated anhydride.
We also applied the Lewis acid-catalyzed anhydride-insertion process to the reaction of polyethers and acyclic anhydrides to make glycol diesters (U.S. Pat. No. 5,254,723). Using this process, a relatively crude polyether polyol mixture can be converted with acetic anhydride to a mixture of glycol diacetates. The glycol diacetates are easily purified by distillation, and can be used as solvents or chemical intermediates.
Unfortunately, the Lewis acid-catalyzed insertion process has its disadvantages. First, the activity of Lewis acids in the process is somewhat lower than desirable. Typically, at least about 1 wt. % of the Lewis acid catalyst is needed for good activity in making the polyetherester. Second, the polyetherester products often have a higher degree of color than is desirable. Third, the presence of high levels of residual Lewis acid catalysts in the polyetherester product can have an unfavorable impact on performance in various end uses. Finally, Lewis acids are often not satisfactory for use in manufacturing operations because they tend to attack reactors and other processing equipment.
An improved process for making polyetheresters by anhydride insertion is needed. Preferably, the process could be used, like the Lewis acid-catalyzed process, to make a wide variety of polyetheresters. Preferably, the process would use low catalyst levels to reduce catalyst costs and minimize the impact of residual catalyst on polyetherester performance. A preferred process would give low-color products. In addition, a process that could be used with ordinary reactors and manufacturing equipment is needed.